Antimicrobial superabsorbent compositions

ABSTRACT

A composition has an enzyme that is able to convert a substrate to release hydrogen peroxide; a substrate for the enzyme; and a superabsorbent component, such as a superabsorbent polymer. The composition is in the form of a powder and may form a gel on contact with water.

This invention relates to compositions for generating antimicrobial activity, particularly compositions that are able to generate hydrogen peroxide.

Honey has been used for treatment of microbial infections since ancient times. In recent years there has been a resurgence of interest in the therapeutic efficacy of honey, particularly in the area of wound healing. Clinical trials have shown that honey is an effective broad-spectrum antimicrobial agent which is effective against common wound-infecting organisms, such as Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans and Escherichia col, and is effective against antibiotic-resistant strains of bacteria. As a natural product, honey also offers an attractive alternative to drug-based treatments.

Many different types of honey have antimicrobial activity. This activity is attributed largely to osmolarity. pH, hydrogen peroxide production and the presence of phytochemical components.

The applicant has appreciated that the antimicrobial effects of honey can be greatly enhanced and controlled by adding glucose oxidase to honey, and that compositions comprising honey and added glucose oxidase are applicable in the treatment of a number of infections, and notably in the treatment of infections caused by biofilms (see WO 2015/166197, WO 2016/083798 and WO 2016/124926). The applicant has also appreciated that beneficial effects may be afforded by compositions that produce low levels of hydrogen peroxide over an extended period of time, and which are storage-stable.

There is a continuing desire to provide antimicrobial products which are effective but also convenient, particularly in the field of wound care and infections, such as chronic and unresolved infections, and at surgical sites.

In a broad sense, the invention concerns hydrogen peroxide-generating compositions which comprise an enzyme that is able to convert a substrate to release hydrogen peroxide, and a substrate for the enzyme. Alternatively or additionally to the substrate, the composition may comprise a precursor-substrate that can be converted to a substrate for the enzyme. The invention also concerns such hydrogen peroxide-generating compositions comprising a water-absorbing component or material.

Preferably, the water-absorbing component is capable of forming a gel on contact with water. For example, the water-absorbing component may be a hydrophilic or hygroscopic powder. The water-absorbing component may be a polymer.

It is preferable that compositions of the invention do not comprise sufficient free water to enable the enzyme to convert the substrate.

According to the invention, there is provided a composition comprising an enzyme that is able to convert a substrate to release hydrogen peroxide, a substrate for the enzyme and a water-absorbing material or component, wherein the composition does not comprise sufficient free water to enable the enzyme to convert the substrate.

According to the invention, there is provided a composition comprising an enzyme that is able to convert a substrate to release hydrogen peroxide, a precursor-substrate that can be converted to a substrate for the enzyme, and a water-absorbing material or component, wherein the composition does not comprise sufficient free water to enable the precursor-substrate to be converted to the substrate or to allow the enzyme to convert the substrate.

In a particularly preferred embodiment, the composition is in the form of a powder.

According to the invention, there is provided a composition comprising an enzyme that is able to convert a substrate to release hydrogen peroxide, a substrate for the enzyme and a water-absorbing material or component, wherein the composition is in the form of a powder.

According to the invention, there is provided a composition comprising an enzyme that is able to convert a substrate to release hydrogen peroxide, a precursor-substrate that can be converted to a substrate for the enzyme, and a water-absorbing material or component, wherein the composition is in the form of a powder.

On contact with a fluid, such as wound exudate, the composition may absorb the fluid to form a gel, such as a hydrogel. The get may produce hydrogen peroxide. As well as producing hydrogen peroxide, the gel may also provide a protective covering for a wound which may prevent or reduce the chance of infection and/or may assist healing. The gel may readily adhere to the wound and/or the tissue surrounding a wound. So, in effect, the gel may form a wound dressing that could be used alone or in conjunction with other dressing materials. The application of a powder may mean that fluid can be absorbed rapidly and a gel can form quickly, which may be particularly beneficial for treating wounds in the field, such as use by the military or the emergency services.

Preferably, the water-absorbing component has an absorption capacity or swelling capacity (which may also be termed free-absorbency capacity, free swelling capacity, fluid retention capacity or water-retention capacity) of 1 g of water, or aqueous solution, per gram of composition (i.e. 1 g/g), or higher. More preferably, the absorption capacity is 5 g/g, or higher. Even more preferably the absorption capacity is 10 g/g or higher. Typically, a superabsorbent material has an absorption capacity of at least 10 g/g. For example in some embodiments, the absorption capacity may be at least 15 g/g. In some embodiments, the absorption capacity may be at least 20 g/g. In some embodiments, the absorption capacity may be at least 30 g/g. In some embodiments, the absorption capacity may be at least 50 g/g. In some embodiments, the absorption capacity may be at least 100 g/g. In some embodiments, the absorption capacity may be at least 200 g/g. In some embodiments, the absorption capacity may be at least 500 g/g. In some embodiments, the absorption capacity may be at least 1000 g/g. Absorption capacity may also be termed centrifuge retention capacity.

The absorption capacity of a water-absorbing material can be measured by methods known to the skilled person.

In one method of measuring absorption capacity, the ‘tea bag’ method, an amount of the material is placed into a tea bag (acrylic/polyester gauze with fine meshes) and the bag is dipped in an excess amount of water or saline solution for one hour to reach equilibrium swelling. The excess solution is removed by hanging the bag until no more liquid drops off. The tea bag is then weighed and the swelling capacity is calculated as follows:

(W₁−W₀)/W₀

W₁ is the weight of the swollen sample and W₀ is the original weight of the material.

Water-retention capacity may be measured in deionised water. Alternatively, water-retention capacity may be measured in a saline solution, such as a 0.9 wt % saline solution.

In another method to measure absorption capacity, the centrifuge method, 0.2 g (W₁), of the material is placed into a bag (60×60 mm) made of non-woven fabric. The bag is dipped in 100 mL of saline solution (0.9% by weight) for half an hour at room temperature. It is taken out, and then excess solution is removed by a centrifugal separator for 3 minutes at 250 g, then the weight of the bag (W₂) is measured. The same stages are carried out with an empty bag and the weight of the bag (W₀) is measured. The water-absorbing capacity is measured as follows:

(W₂−W₀−W₁)/W₁

This test (NWSP 241.0R2) is standardised by the European Disposables and Nonwovens Association (EDANA).

In a particularly preferred embodiment, the water-absorbing component is a superabsorbent material or component.

According to the invention, there is provided a composition comprising an enzyme that is able to convert a substrate to release hydrogen peroxide; a substrate for the enzyme; and a superabsorbent material or component.

According to the invention, there is provided a composition comprising an enzyme that is able to convert a substrate to release hydrogen peroxide; a substrate for the enzyme; and a superabsorbent material or component, wherein the composition is in the form of a powder.

According to the invention, there is provided a composition comprising an enzyme that is able to convert a substrate to release hydrogen peroxide; a precursor-substrate that can be converted to a substrate for the enzyme; and a superabsorbent material or component, wherein the composition is in the form of a powder.

The superabsorbent component may be a superabsorbent polymer (SAP). SAPs are polymers that can absorb and retain extremely large amounts of liquid relative to their own mass. SAPS are usually made from hydrophilic polymers containing anionic water-holding groups, such as carboxylic acid groups. Commonly, SAPs are produced from acrylic acid, its salts, or acrylamide. SAPs are preferably cross-linked, with the degree and type of cross-linking affecting its properties. For example, low-density cross-linked SAPs generally have higher water-retention capacity and swell to a larger degree, but may have a softer and stickier gel formation. High cross-link density polymers may exhibit lower water retention capacity, but may provide a firmer gel that is able to retain its shape more readily.

SAPs may be classified according to the charge in the cross-linked chains. For example, the SAP may be non-ionic, ionic, amphoteric or zwitterionic. In some preferred embodiments, the hydrogels are anionic.

Conventional SAPs useful for compositions according to the invention include polyacrylates and polyacrylamides, such as cross-linked polyacrylates and polyacrylamides. A particularly preferred SAP is sodium polyacrylate.

The SAP may be selected from the group consisting of: a hydrolysed cellulose-polyacrylonitrile; a starch-polyacrylonitrile co-polymer; a cross-linked co-polymer of maleic anhydride, such as ethylene maleic anhydride co-polymer; cross-linked carboxymethyl cellulose; polyvinyl alcohol co-polymer; and cross-linked polyethylene oxide.

Although synthetic polymer-based SAPs may be preferred, polysaccharide-bases SAPs and poly(amino acid)-based SAPs may also be used.

Compositions of the invention may comprise 0.5 to 75% by weight of the water-absorbing component (e.g. superabsorbent component). Compositions of the invention may comprise 1 to 50% by weight of the water-absorbing component. Compositions of the invention may comprise 2 to 30% by weight of the water-absorbing component. Compositions of the invention may comprise at least 0.5% by weight of the water-absorbing component. Compositions of the invention may comprise 50% by weight, or less, of water-absorbing component. Compositions of the invention may comprise 2% by weight, or more, of the water-absorbing component.

Compositions of the invention may comprise 30% by weight, or less, of the water-absorbing component.

Compositions of the invention may comprise at least 10% by weight of the water-absorbing component. Compositions of the invention may comprise at least 25% by weight of the water-absorbing component. Compositions of the invention may comprise 75% by weight, or less of water-absorbing component. Compositions of the invention may comprise 25% to 75% by weight of the water-absorbing component.

If the composition is in the form of a powder, the particle size may be adjusted to optimise the composition according to its intended application. For example, the smaller the particle size, the more easily it may become solubilised or absorb fluid. However, it may be undesirable for the particle size to be too small such that a significant amount becomes aerosolised upon dispensing.

The powder may have a mean particle size of 3000 μm or less. The powder may have a mean particle size of 2000 μm or less. The powder may have a mean particle size of 1000 μm or less. The powder may have a mean particle diameter of 500 μm or less.

The powder may have a mean particle size of 50 μm or more. The powder may have a mean particle size of 100 μm or more. The powder may have a mean particle size of 200 μm or more.

For example, the powder may have a mean particle size of 50 to 3000 μm. The powder may have a mean particle size of 100 to 2000 μm. The powder may have a mean particle size of 100 to 1000 μm.

The powder may contains less than 10% of particles with a size of 1000 μm or more. The powder may contain less than 10% of particles with a size of 50 μm or less.

The powder may have a modal particle size of 3000 μm or less. The powder may have a modal particle size of 2000 μm or less. The powder may have a modal particle size of 1000 μm or less. The powder may have modal particle size of 500 μm or less.

The powder may have a modal particle size of 50 μm or more. The powder may have a modal particle size of 100 μm or more. The powder may have a modal particle size of 200 μm or more.

For example, the powder may have a modal particle size of 50 to 3000 μm. The powder may have a modal particle size of 100 to 2000 μm. The powder may have a modal particle size of 100 to 1000 μm.

Particle size is conventionally reported in terms of diameter irrespective of the actual particle shape; commonly the equivalent sphere diameter, defined by ISO 9276-1. Particle size analysis may be undertaken, for example, by image analysis using equivalent projected circle area or Feret diameters.

The powder may have a polymodal, (e.g. bimodal or trimodal) particle distribution.

The powder may have a peak sphericity of 0.8 or higher, 0.85 or higher or 0.9 or higher.

Compositions of the invention may comprise an unrefined substance that includes the substrate for the enzyme. The term “unrefined” is used herein to refer to substances that have not been processed into a pure form. Unrefined substances include substances that may have been concentrated, for example by drying or boiling. The substance may include one or more substrates from a natural source (termed herein a “natural substance”). Examples of natural substances include substances from a plant source, including from sap, roots, nectar, flowers, seeds, fruit, leaves, or shoots. The substance may be an unrefined natural substance, such as honey.

If compositions of the invention do comprise honey, the honey may be pasteurised. The honey may not contain catalase activity. The honey may be creamed. The honey may be a dried honey, such as a powdered honey.

In compositions of the invention that comprise honey, the honey may account for at least 10% by weight of the composition. In a more preferred embodiment, the honey many account for at least 25% by weight of the composition. In an even more preferred embodiment, the honey may account for at least 40% by weight of the composition. Honey may account for 10 to 80% by weight of the composition. For example, honey may account for 25 to 75% by weight of the composition.

Because honey is a natural product, its composition can vary greatly depending on its source. For example, the difference in antimicrobial potency among honeys can be more than one hundred-fold, depending on the geographical, seasonal and botanical source of the honey, as well as the harvesting, processing and storage conditions. Consequently, the antimicrobial efficacy may also vary depending on the type of honey used. Furthermore, honey may also contain other components, such as allergens e.g. trace amounts of pollen, which may cause adverse reactions when applied to certain subjects and make it unsuitable for certain pharmaceutical applications.

Honey may require processing such that it is in a suitable form for application to subjects, which can add cost and complexity to the production process. Such processing may include creaming or pasteurisation. Furthermore, for certain pharmaceutical applications, it may be difficult to get regulatory approval for honey-based compositions.

Consequently, although compositions based on natural products, such as honey-based compositions, may be used in compositions of the invention, there is a desire to provide improved compositions which provide some of the antimicrobial benefits provided by honey, but which also overcome some of its disadvantages.

So, the invention also concerns compositions that do not comprise an unrefined natural substance such as honey. For example, the compositions of the invention may comprise a purified enzyme that is able to convert a substrate to release hydrogen peroxide; and a purified substrate for the enzyme (or a purified precursor substrate that can be converted to a substrate for the enzyme).

Surprisingly, the applicant has found that compositions comprising a purified enzyme and a purified substrate or purified precursor-substrate can be more effective at killing microorganisms than known honey-based compositions that can generate hydrogen peroxide.

Consequently, according to the invention, there is provided a composition for generating hydrogen peroxide comprising: a purified enzyme that is able to convert a substrate to release hydrogen peroxide; a purified substrate for the enzyme; and a superabsorbent component.

According to the invention, there is provided a composition for generating hydrogen peroxide comprising: a purified enzyme that is able to convert a substrate to release hydrogen peroxide; a purified substrate for the enzyme; and a superabsorbent component, wherein the composition is in the form of a powder.

According to the invention, there is provided a composition for generating hydrogen peroxide comprising: a purified enzyme that is able to convert a substrate to release hydrogen peroxide; a purified precursor-substrate that can be converted to a substrate for the enzyme; and a superabsorbent component.

According to the invention, there is provided a composition for generating hydrogen peroxide comprising: a purified enzyme that is able to convert a substrate to release hydrogen peroxide; a purified precursor-substrate that can be converted to a substrate for the enzyme; and a superabsorbent component, wherein the composition is in the form of a powder.

Preferably, the enzyme is an oxidoreductase enzyme. Examples of oxidoreductase enzymes that can convert a substrate to release hydrogen peroxide include glucose oxidase, hexose oxidase, cholesterol oxidase, galactose oxidase, pyranose oxidase, choline oxidase, pyruvate oxidase, glycollate oxidase, and amioacid oxidase. The corresponding substrates for these oxidoreductase enzymes are D-glucose, hexose, cholesterol, D-galactose, pyranose, choline, pyruvate, glycollate and aminoacid, respectively.

A mixture of one or more oxidoreductase enzymes and one or more substrates for the oxidoreductese enzymes may be present in a composition of the invention.

According to a preferred embodiment of the invention, the oxidoreductase enzyme is glucose oxidase and the substrate is D-glucose.

References herein to “enzyme” refer to one or more enzyme. For example, in some embodiments, compositions of the invention may comprise a plurality of enzymes that are able to convert a substrate to release hydrogen peroxide, in some embodiments, compositions of the invention may comprise only one enzyme that is able to convert a substrate to release hydrogen peroxide.

The term “purified enzyme” is used herein to include an enzyme preparation in which the enzyme has been separated from at least some of the impurities originally present when the enzyme was produced. Preferably, impurities that have been removed or reduced include those that would otherwise interfere with the ability of the enzyme to convert the substrate to release hydrogen peroxide.

It may not always be necessary or desirable that the purified enzyme is at a high level of purity provided that the enzyme is able to convert the substrate to release hydrogen peroxide. In some circumstances, it may be desirable to use a relatively crude enzyme preparation. Examples of suitable purity levels include at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% pure (mass purity). Preferably, the enzyme is at least 90% pure. Even more preferably, the enzyme is at least 99% pure.

The enzyme may have been produced by recombinant or non-recombinant means, and may be a recombinant or non-recombinant enzyme. The enzyme may be purified from a microbial source, preferably from a non-genetically modified microbe.

The level of purity of the enzyme may be selected as appropriate depending on the intended use of the composition. For medical use, a medical grade or medical device grade of purity may be used. For pharmaceutical use, a pharmaceutical grade of purity may be used.

Compositions of the invention may comprise sufficient enzyme and substrate to provide for sustained release of hydrogen peroxide at a specific level or concentration.

Compositions of the invention may comprise sufficient enzyme and substrate to provide for sustained release of hydrogen peroxide at a level of less than 2 mmol/litre for a period of at least twenty four hours, following dilution of the composition.

Compositions of the invention may comprise sufficient enzyme and substrate to provide for sustained release of at least 0.02, 0.03, 0.04, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 1 or 1.5 mmol/litre hydrogen peroxide for a period of at least 24 hours, more preferably 48 hours.

So, in some embodiments, compositions of the invention may comprise sufficient enzyme and substrate to provide for sustained release of 0.1 to 2 mmol/litre hydrogen peroxide for a period of at least 24 hours, more preferably 48 hours.

For example, in some embodiments, compositions of the invention may provide for sustained release of hydrogen peroxide at a concentration of at least 2 ppm, at least 5 ppm, at least 10 ppm, at least 20 ppm or at least 50 ppm. In preferred embodiments, the level may be at least 2 ppm. In some embodiments, the concentration may be, at the most, 500 ppm, 200 ppm, 100 ppm, 50 ppm, 20 ppm or 10 ppm. In preferred embodiments, the level may be 20 ppm or less. In even more preferred embodiments, the level may be 10 ppm or less. For example, the concentration may be 10 to 500 ppm, 20 to 200 ppm or 50 to 100 ppm, 2 to 50 ppm, 2 to 20 ppm or 5 to 10 ppm. If the composition does not comprise sufficient free water to allow the enzyme to convert the substrate (e.g. If the composition is a dry or dried composition), hydrogen peroxide production may only occur once it has been diluted by water and there is sufficient free water to allow the enzyme to convert the substrate. Addition of water may thus initiate hydrogen peroxide production. Compositions, of the invention may provide for sustained release of hydrogen peroxide for at least 1 hour, at least 12 hours, at least 24 hours, at least 2 days, or at least 4 days. Preferably, the level of hydrogen peroxide is sustained for at least 4 days. In preferred embodiments, the level of hydrogen peroxide is sustained at 10 to 500 ppm for at least 1 hour, at least 12 hours, at least 24 hours, at least 2 days, or at least 4 days. In other embodiments, the level of hydrogen peroxide is sustained at 50 to 100 ppm for at least 1 hour, at least 12 hours, at least 24 hours, at least 2 days, or at least 4 days. In other embodiments, the level of hydrogen peroxide is sustained at 2 to 50 ppm for at least 12 hours, at least 24 hours, at least 2 days, or at least 4 days. In other embodiments, the level of hydrogen peroxide is sustained at 5 to 10 ppm for at least 12 hours, at least 24 hours, at least 2 days, or at least 4 days. In some embodiments, compositions of the invention may provide for sustained release of 2 to 500 ppm hydrogen peroxide for at least 24 hours.

Compositions of the invention may comprise 25 to 2000 ppm of the enzyme, for example 50 to 1000 ppm of the enzyme. Compositions of the invention may comprise 750 to 2000 ppm of the enzyme. Compositions of the invention may comprise at least 500 ppm of the enzyme. Compositions of the invention may comprise 250 to 1500 of the enzyme.

The enzyme activity (for example, the glucose oxidase activity) may range, for example, from 1-400 IU/mg, or 1-300 IU/mg, for example 250-280 IU/mg. The amount of enzyme used is likely to depend on several factors, including the desired use of the composition, the desired level of hydrogen peroxide release, and the desired length of time for hydrogen peroxide release. A suitable amount of enzyme can readily be determined by a person of ordinary skill in the art, if necessary using a well diffusion assay, to determine the extent of hydrogen peroxide release for different amounts of enzyme. Suitable amounts of enzyme (such as glucose oxidase) may be from 0.0001% to 0.5% w/w of the composition. The amount of enzyme used may be selected so as to produce a composition for generating antimicrobial activity that is equivalent to a selected phenol standard (for example a 10%, 20%, or 30% phenol standard).

Compositions of the invention may comprise at least 1 unit, and preferably up to 1500 units, of the enzyme per gram of the composition. A “unit” is defined herein as the amount of enzyme (e.g. glucose oxidase) causing the oxidation of 1 micromole of substrate (e.g. glucose) per minute at 25 degrees centigrade at pH 7.0.

In some embodiments, a composition according to the invention comprises more than 15 units, for example at least 30 units, at least 50 units, or at least 100 units, and suitably less than 685 units, for example 100-500 units, of enzyme (e.g. glucose oxidase) per gram of the composition.

In other embodiments of the invention, a composition according to the invention comprises at least 500 units, for example 500-1000 units, or 685-1000 units, of enzyme (e.g. glucose oxidase) per gram of the composition.

References herein to “substrate” or precursor-substrate” refer to one or more substrate. For example, in some embodiments, compositions of the invention may comprise a plurality of substrates or precursor-substrates. In some embodiments, compositions of the invention may comprise only one substrate or only one precursor substrate.

The term “purified substrate” or “purified precursor-substrate” is used herein to include a substrate or precursor-substrate preparation in which the substrate or precursor-substrate has been separated from at least some of the impurities originally present when the substrate or precursor-substrate was obtained or produced. The purified substrate or precursor-substrate may be obtained from a natural source or may be synthetically produced. The purified substrate or precursor-substrate may be a processed, extracted, or refined substrate or precursor-substrate (i.e. a substrate or precursor-substrate in which impurities or unwanted elements have been removed by processing).

It may not always be necessary or desirable that the purified substrate or precursor substrate is at a high level of purity provided that the enzyme is able to convert the substrate to release hydrogen peroxide. In some circumstances, it may be desirable to use a relatively crude substrate or precursor-substrate preparation. Examples of suitable purity levels include at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or 99% pure. Preferably the purity level is at least 90%, even more preferably at least 99%. However, in some embodiments, it may be desirable that the purified substrate or purified precursor-substrate is a medical grade, medical device grade, or pharmaceutical grade substrate or precursor-substrate.

In particular embodiments, the purified substrate or precursor substrate is or comprises a purified sugar. The term “sugar” is used herein to refer to a carbohydrate with the general formula C_(m)(H₂O)_(n). The purified sugar may be obtained from a natural source (for example a processed, extracted, or refined natural sugar), or be synthetically produced. The purified sugar may be at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or 99% pure. Preferably, the purity level is at least 90%. Even more preferably, the purity level is at least 99%. The purified sugar may be a medical grade, medical device grade, or pharmaceutical grade sugar. The sugar may include, for example purified D-glucose, hexose, or D-galactose. For example, the purified sugar may be medical grade, medical device grade, or pharmaceutical grade D-glucose, hexose, or D-galactose.

In particular embodiments, the enzyme and the substrate are purified, for example purified glucose oxidase and purified D-glucose, suitably medical grade, medical device grade, or pharmaceutical grade glucose oxidase and D-glucose.

For compositions of the invention which comprise a precursor-substrate, the composition preferably comprises one or more enzymes (preferably purified enzymes) for converting the precursor-substrate to the substrate for the enzyme. However, in some embodiments, the precursor-substrate may not necessarily be converted to the substrate enzymatically. For example, for some precursor substrates, addition of water may be sufficient for conversion. Alternatively or additionally, compositions of the invention may comprise non-enzymatic catalysts.

So, compositions of the invention which comprise a precursor-substrate may comprise a first enzyme that is able to convert the substrate to release hydrogen peroxide, and a second enzyme that is able to convert the precursor-substrate to the substrate for the first enzyme.

The precursor-substrate is preferably a carbohydrate, such as a polysaccharide, or a sugar e.g. a disaccharide, or sugar derivative.

For example, the precursor-substrate may be sucrose, the first enzyme may be glucose oxidase and the second enzyme may be invertase.

In another example, the precursor-substrate may be maltose, the first enzyme may be glucose oxidase and the second enzyme may be maltase.

Compositions of the invention which comprise a precursor-substrate may comprise an enzyme (preferably a purified enzyme) that is able to convert the substrate to release hydrogen peroxide, and at least two enzymes (e.g. second and third enzymes, preferably purified enzymes) that are able to convert the precursor-substrate to the substrate for the first enzyme.

For example, the precursor-substrate may be starch, the first enzyme may be glucose oxidase and the second and third enzymes may be amylase and maltase.

For example, the precursor-substrate may be cellulose, the first enzyme may be glucose oxidase and the second and third enzymes may be cellulose and beta-glucosidase.

In some embodiments, compositions of the invention may comprise both a substrate that can be converted by the enzyme to generate hydrogen peroxide, and a precursor-substrate that can be converted to the substrate.

Although compositions of the invention preferably do not include sufficient free water to allow the enzyme to convert the substrate, in some embodiments, compositions of the invention may comprise sufficient free water to allow the enzyme to convert the substrate.

Compositions of the invention may comprise freeze-drying protective agents. This is because compositions of the invention can be formed by freeze-drying. Preferably, the freeze-drying protective agent is a sugar or polysaccharide. In some embodiments the freeze-drying protective agent comprises cyclodextrin (e.g. methylated β-cyclodextrin) and/or maltodextrin. Other suitable freeze-drying protective agents may include polyethylene glycol, dextran, hydroxyethyl starch, ficoll, gum Arabic, gelatin, polyvinylpyrrolidone, cellulose, methocel, sepadex or bovine serum albumin.

If compositions of the invention comprise a freeze-drying protective agent, the freeze-drying protective agent may be present in an amount of 25 to 75% by weight, for example 30 to 60% by weight.

In one embodiment, a composition of the invention may comprise 25 to 75% by weight unrefined natural substrate (e.g. honey), 25 to 75% by weight freeze-drying protective agent and 2 to 25% superabsorbent component. For example, a composition of the invention may comprise 30 to 50% by weight unrefined natural substrate (e.g. honey), 30 to 50% by weight freeze-drying protective agent and 4 to 25% superabsorbent component.

In one embodiment, a composition of the invention may comprise 25 to 75% by weight sugars (e.g. glucose+fructose), 25 to 75% by weight freeze-drying protective agent and 2 to 25% superabsorbent component. For example, a composition of the invention may comprise 30 to 50% by weight sugars (e.g. glucose+fructose), 30 to 50% by weight freeze-drying protective agent and 4 to 25% superabsorbent component.

In one embodiment, a composition of the invention may comprise 25 to 75% by weight of substrate and solute combined (e.g. glucose+fructose), 25 to 75% by weight freeze-drying protective agent and 2 to 25% superabsorbent component. For example, a composition of the invention may comprise 30 to 50% by weight substrate and solute combined (e.g. glucose+fructose), 30 to 50% by weight freeze-drying protective agent and 4 to 25% superabsorbent component.

Compositions of the invention may not comprise a freeze-drying protective agent.

In one embodiment, a composition of the invention may comprise 50 to 95% by weight honey and 5 to 50% superabsorbent component.

In one embodiment, a composition of the invention may comprise 50 to 95% by weight sugars and 5 to 50% superabsorbent component.

In one embodiment, a composition of the invention may comprise 50 to 95% by weight substrate and solute combined, and 5 to 50% superabsorbent component.

Compositions of the invention may be storage-stable. The term ‘storage-stable’ is used herein to mean that the composition can be stored at ambient temperature for at least several days, preferably at least a week, more preferably at least one or two months, whilst retaining the ability to generate antimicrobial activity following dilution of the composition. A preferred storage temperature is below 37° C., preferably 20-25° C. Preferably compositions are stored away from exposure to light.

Hydrogen peroxide is generally unstable at ambient temperature. The lack of sufficient free water in some compositions of the invention may thus prevent the enzyme converting the substrate to release hydrogen peroxide, and thus helps to maintain the stability of the composition for extended periods at ambient temperature. A composition of the invention may include some water provided that there is not sufficient free water to allow the enzyme to convert the substrate. Suitable amounts of water will vary depending on the precise components of the composition. However, typically, a storage-stable composition of the invention preferably comprises less than 20% (by weight) total water content, for example, 10%-19%, water. Compositions of the invention may comprise 12% or less (by weight) of water. Compositions of the invention may comprise 10% or less (by weight) of water. Compositions of the invention may comprise 5% or less (by weight) of water. Compositions of the invention may comprise 3% or less (by weight) of water. Compositions of the invention may comprise 1% or less (by weight) of water.

For compositions of the invention that do contain sufficient free water to allow the enzyme to convert the substrate, water may be present in an amount which is at least 20% by weight, or at least 30% by weight.

The skilled person would understand that if a composition of the invention does not comprise sufficient free water to allow the enzyme to convert the substrate, it may contain trace amounts of free water that may allow trace amounts, or substantially no, hydrogen peroxide to be produced. Hydrogen peroxide may be present in the composition at a concentration of 120 μM or less, preferably 100 μM or less, more preferably 80 μM or less. Once the composition is diluted, hydrogen peroxide may then be generated at substantial concentrations.

Preferably, compositions of the invention comprise substantially no hydrogen peroxide, trace amounts of hydrogen peroxide or no detectable hydrogen peroxide. For example, hydrogen peroxide is preferably not detectable using a hydrogen peroxide test strip, such as a Quantofix® peroxide test stick (Sigma Aldrich, UK). For example, hydrogen peroxide may present at a level less than 1 ppm or at a level less than 0.5 ppm. Hydrogen peroxide may be at a level less than 0.1 ppm.

Compositions of the invention may comprise an additional component which is preferably a solute. References herein to “solute” refer to one or more solute. For example, in some embodiments, compositions of the invention may comprise a plurality of solutes. In some embodiments, the composition may only comprise one solute. Preferably the solute is soluble in water.

The solute may be distinct from the substrate, or in some examples, the substrate may be same as the solute. For example, the composition may comprise fructose and fructose oxidase: the fructose being both the solute and the substrate for enzyme. In another example, the substrate may be glucose and the solute may be fructose.

The solute is preferably purified, meaning that the solute has been separated from at least some of the impurities originally present when the solute was obtained or produced. The purified solute may be obtained from a natural source or may be synthetically produced. The purified solute may be a processed, extracted, or refined substrate (i.e. a solute in which impurities or unwanted elements have been removed by processing).

It may not always be necessary or desirable that the purified solute is at a high level of purity. In some circumstances, it may be desirable to use a relatively crude solute preparation. Examples of suitable purity levels include at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or 99% pure. Preferably, the purity level is at least 90%. Even more preferably, the purity level is at least 99%. However, in some embodiments, it may be desirable that the solute is a medical grade, medical device grade, or pharmaceutical grade solute.

The solute may be a carbohydrate. The solute may be a polysaccharide. Preferably, the solute is a sugar or sugar derivative. More preferably, the solute is a sugar. Suitable sugars include oligosaccharides, disaccharides or monosaccharides. Preferably, the sugar is a disaccharide or a monosaccharide. In particularly preferred embodiments, the sugar is a monosaccharide. Suitable sugars may include fructose, glucose, galactose, sucrose and maltose. In a particularly preferred embodiment, the sugar is fructose.

The term “sugar derivative” is used herein to refer to a sugar that has been modified by addition of one or more substituents other than a hydroxyl group. Sugar derivatives, thus encompass amino sugars, acidic sugars, deoxy sugars, sugar alcohols, glycosylamines and sugar phosphates. For example, sugar derivatives may include glucose-6-phosphateglucosamine, glucoronate, gluconate, galactosamine, glucosamine, sialic acid, deoxyribosefucose, rhamnose glucuronic acid, polyols (e.g. sorbitol, erythritol, xylitol, mannitol, lactitol and maltitol) and sucralose.

Compositions of the invention may comprise two or more solutes, as described herein. For example, compositions of the invention may comprise two or more sugars or sugar derivatives. The composition may comprise a maximum of two solutes, e.g. two sugars or sugar derivatives; or a maximum of three solutes, e.g. three sugars or sugar derivatives. For instance, a composition of the invention may comprise glucose, fructose and sucrose.

The solute preferably has a high solubility in water, for example a solubility which is greater than glucose. Glucose has a solubility of 90 g/100 g water at 20° C. and 1 atm. In a preferred embodiment, the solute has a solubility greater than or equal to 100 g/100 g water at 20° C. and 1 atm, in a more preferred embodiment, the solute has a solubility greater than or equal to 200 g/100 g water at 20° C. and 1 atm, in an even more preferred embodiment, the solute has a solubility greater than 300 g/100 g water at 20° C. and 1 atm.

A solute with a high solubility may be advantageous because if the composition of the invention is a solution, it may enable the solution to have a high concentration of solutes, which may in turn provide a high osmolarity or osmotic strength. Compositions with a high osmolarity or osmotic strength may assist with the antimicrobial efficacy of the composition because they may reduce the amount of water available for microbes or draw water away from microbes, and may assist in wound healing and wound debridement.

Fructose is a particularly preferred solute because it has a solubility of about 375 g/100 g water at 20° C. and 1 atm. Consequently, the solute may be fructose.

In some embodiments, the solute with a solubility of at least 100 g/100 g water at 20° C. and 1 atm, at least 200 g/100 g water at 20° C. and 1 atm or at least 300 g/100 g water at 20° C. and 1 atm. may be the purified substrate. So, for example, a composition of the invention may comprise fructose and fructose oxidase.

Compositions of the invention may thus comprise only one sugar or sugar derivative which is the solute and the substrate, and one enzyme for converting the substrate and generating hydrogen peroxide.

In some embodiments, the solute with the solubility of at least 100 g/100 g water at 20° C. and 1 atm, at least 200 g/100 g water at 20° C. and 1 atm or at least 300 g/100 g water at 20° C. and 1 atm, may be distinct from the purified substrate. For example, a composition of the invention may comprise glucose, glucose oxidase and fructose.

In preferred embodiments, the purified substrate is a sugar or sugar derivative (e.g. glucose) and the solute is a sugar or sugar derivative (e.g. fructose).

Preferably, the composition comprises at least two sugars or sugar derivatives (e.g. including glucose and fructose). The composition may comprise a maximum of two sugars or sugar derivatives (e.g. only glucose and fructose).

Compositions of the invention may comprise at least 5% by weight of sugars and/or sugar derivatives. Compositions of the invention may comprise at least 10% by weight of sugars and/or sugar derivatives. Compositions of the invention may comprise at least 25% by weight of sugars and/or sugar derivatives. Compositions of the invention may comprise at least 50% by weight of sugars and/or sugar derivatives. Compositions of the invention may comprise 95% by weight or less of sugars or sugar derivatives. Compositions of the invention may comprise at 75% by weight or less of sugars and/or sugar derivatives. For example, compositions of the invention may comprise 10% to 95% by weight sugars and/or sugar derivatives. Compositions of the invention may comprise 25% to 75% by weight sugars and/or sugar derivatives. Compositions of the invention may comprise 50 to 95% by weight sugars and/or sugar derivatives.

Compositions of the invention may comprise 5 to 50% by weight of substrate for the enzyme (e.g. glucose) or 5 to 50% by weight of the precursor substrate that can be converted to the substrate for the enzyme. For instance, compositions of the invention may comprise 5 to 25% by weight of substrate for the enzyme (e.g. glucose) or 5 to 25% by weight of the precursor substrate that can be converted to the substrate for the enzyme

Compositions of the invention may comprise 5 to 75% by weight of solute (e.g. fructose). For instance, compositions of the invention may comprise 10 to 50% by weight of solute.

Compositions of the invention may comprise a buffer, or a component that may be capable of acting as act as a buffer in an aqueous solution. An example of a suitable buffer is a citric acid/NaOH buffer, such as a 50 mMol citric acid/NaOH buffer. Compositions of the invention may be buffered (or may be capable of being buffered in an aqueous solution) at a pH of 5 or less. e.g. 3 to 5 (such as about pH 4). Alternatively, compositions of the invention may be buffered (or may be capable of being buffered in an aqueous solution) at a pH greater than 5, e.g. 6 to 8 (such as about pH 7).

Compositions of the invention preferably comprise substantially no peroxidase, or are essentially free of peroxidase.

Compositions of the invention preferably comprise substantially no zinc oxide, or are essentially free of zinc oxide.

A composition of the invention may comprise at least one suitable antimicrobial or immunostimulatory component, excipient or adjuvant, or any other suitable component where it is desired to provide ability to generate antimicrobial activity. Compositions of the invention may not comprise an antibiotic.

Compositions of the invention may comprise a salt.

Compositions of the invention may comprise a blood clotting agent. For example, compositions of the invention may comprise a coagulation factor. Potential coagulation factors include fibrinogen or thrombin. Artificial blood clotting agents could be included in compositions of the invention. Examples of such agents include carriers, such as albumin carriers, to which fibrinogen-binding peptides are immobilised.

Compositions of the invention are preferably sterile. Compositions of the invention may be sterilised by any suitable means. Preferably compositions of the invention have been sterilised by irradiation. The Applicant has found that compositions can retain glucose oxidase activity (and, therefore, the ability to release hydrogen peroxide on dilution) following sterilization by exposure to gamma radiation or electron beam radiation. A suitable level of gamma irradiation is 10-70 kGy, preferably 25-70 kGy, more preferably 35-70 kGy. Alternatively, compositions of the invention may be sterilised by electron beam irradiation. A suitable level or dose of irradiation (e.g. electron beam irradiation) may be 10-100 kGy, preferably 30-80 kGy, more preferably 50-80 kGy. The dose may be greater than 35 kGy. The dose may be less than 80 kGy, for example 75 kGy or less. In one embodiment, compositions of the invention may be sterilised by irradiation that is not gamma irradiation.

There is also provided according to the invention a method of sterilising a composition of the invention, which comprises exposing the composition to irradiation, preferably gamma irradiation or electron beam irradiation.

Since ozone has not been authorised by the US FDA for sterilisation of honey-based products for use in wound healing, compositions according to the invention preferably have not been sterilized by ozonation, and do not include ozone, or any components that have been subjected to sterilisation by ozonation. In particular, compositions according to the invention should not comprise ozonized honey or ozonated oil.

Preferred compositions for medical use according to the invention are sterile, single use compositions.

Sterilised compositions for use according to the invention that are stored away from exposure to light are expected to retain stability for at least six months. For example, such compositions may be packaged in high-density polyethylene/low-density polyethylene (HDPE/LDPE) tubes or in polyester-aluminium-polyethylene (PET/AI/PE) sachets.

A composition of the invention is preferably a medical grade or medical device grade composition. A composition of the invention may be a pharmaceutical grade composition.

A composition of the invention may be provided with a wound dressing material to form a wound dressing. For example, the wound dressing material may be impregnated with the composition or the composition may be immobilised to the wound dressing material. Suitable wound dressing materials include gauzes, bandages, tissues, films, gels, foams, hydrocolloids, alginates, polysaccharide pastes, granules or beads. The composition may be present together with a wound-dressing matrix, such as a collagen or collagen-glycosaminoglycan matrix. The dressing may be a tulle dressing. Compositions in combination with a dressing are preferably sterile, and may be sterilised using irradiation, e.g. gamma irradiation. The wound dressing material may be impregnated with the composition, or the composition may be immobilised on the dressing material, such as on a surface of the dressing material.

The invention may provide a kit comprising a wound dressing material and, separately, a composition of the invention.

A composition of the invention may be provided in a container. Preferably the container is designed such that moisture in the air is prevented from entering the container and being absorbed by the composition. For example, the container may be an airtight container. The container may comprise a dessicant, such as silica gel. The composition in the container is preferably sterile whilst in the container. The container may be opaque.

The container may be designed to enable the composition to be dispensed. For example, the container may define one or a plurality of holes or apertures. The holes or apertures may be covered or sealed prior to use, for example using a cap, such as an airtight cap. The cover or seal may be removable and replaceable. The one or plurality of holes or apertures may permit dispensing of the composition when the container is inverted and shaken by a user.

Alternatively, the container may be a powder spray, such as a pressurised powder spray.

As described above, the composition may form a gel when it is contacted with water or a water-containing fluid, such as an aqueous solution (e.g. a bodily fluid such as wound exudate).

Consequently, according to the invention, there is provided a gel, preferably a hydrogel, comprising an enzyme that is able to convert a substrate to release hydrogen peroxide; a substrate for the enzyme; and a superabsorbent material.

According to the invention, there is provided a gel, preferably a hydrogel, comprising an enzyme that is able to convert a substrate to release hydrogen peroxide; a precursor-substrate that can be converted into a substrate for the enzyme; and a superabsorbent material.

The enzyme, substrate and precursor-substrate may have any of the characteristics as already described herein. For example, it is preferable that the enzyme is a purified enzyme, the substrate is a purified substrate and the precursor-substrate is a purified precursor-substrate.

It is envisaged that the gel could form in situ, such as at the site of the wound, following application of the composition of the invention (e.g. In powder form) to a wound site. However, it is also possible that the gel could be pre-formed before application to a patient. For example, a user may mix the composition with water to form the gel, and then the gel may be applied to a wound site. The gel may be used in conjunction with a wound dressing, such as a gauze, bandage, tissue, film, gel, foam, hydrocolloid, alginate, polysaccharide paste, granules or beads.

Gels of the invention may be more elastic than viscous. So, when viscoelasticity is tested at a specific frequency, say at a frequency from 1 to 10 Hz, the storage modulus may be higher than the loss modulus.

Increasing the amount of superabsorbent component in the composition (e.g. increasing the amount of superabsorbent polymer) may increase the stiffness of the resulting gel.

Compositions of the invention may be used to treat any microbial infection that can be treated by hydrogen peroxide. Examples include infection caused by gram positive bacteria, gram negative bacteria, acid-fast bacteria, viruses, yeasts, parasitic or pathogenic micro-organisms or fungi. For example, infections caused by the following micro-organisms may be treated: Escherichia coli. Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans, Propionibacterium acnes, Staphylococcus aureus. Staphylococcus epidermidis, Staphylococcus saprophytics, Beta haemolytic Streptococci Group A or B, Campylobacter coli, Campylobacter jejuni, Methicillin Resistant Staphylococcus Aureus (MRSA), Methicillin Sensitive Staphylococcus Aureus (MSSA), Botrytis cinerea, Mycobacterium tuberculosis, Cryptosporidium, Plasmodium, Streptococcus pyogenes, streptococcus zooepidemicus and Toxoplasma.

There is further provided according to the invention a composition of the invention for use in the prevention or treatment of a microbial infection, for example a microbial infection that comprises a biofilm, or a microbe that is capable of forming a biofilm. So, there may be provided a compositions of the invention for use in the prevention or treatment of a microbial infection that comprises a bioflim or a microbe that is capable of forming a biofilm. The biofilm may comprise bacteria, fungi and/or viruses.

There is also provided according to the invention use of a composition of the invention in the manufacture of a medicament for the prevention or treatment of a microbial infection, for example a microbial infection that comprises a biofilm, or a microbe that is capable of forming a biofilm.

The invention also provides a method of preventing or treating a microbial infection, for example a microbial infection that comprises a biofilm, or a microbe that is capable of forming a biofilm, wherein the method comprises administering an effective amount of a composition of the invention to a site of the infection.

According to the invention there is also provided use of a composition or solution of the invention to prevent or inhibit microbial growth.

There is also provided according to the invention a composition of the invention for use as a medicament.

Compositions of the invention may be used to treat animals. Compositions of the invention may be used to treat humans.

There is further provided according to the invention a composition of the invention for the prevention, treatment, or amelioration of a microbial infection.

The invention also provides use of a composition or solution of the invention in the manufacture of a medicament for the prevention, treatment, or amelioration of a microbial infection.

There is further provided according to the invention a method of preventing, treating, or ameliorating a microbial infection, which comprises administering a composition or solution of the invention to a subject in need of such prevention, treatment or amelioration. The subject may be a human or animal subject. Compositions of the invention may be topically administered.

Compositions of the invention may be for administration to surgical wounds.

Compositions of the invention with a high osmolarity (suitably having a water activity (a_(w)) in the range similar to honey, i.e. 0.47-0.7) are believed to facilitate the debridement of wounds by the autolytic action of tissue proteases. They may create a moist wound environment by drawing out lymph fluid from the wound tissues through their strong osmotic action. This provides a constant supply of proteases at the interface of the wound bed and the overlying necrotic tissue. This action also washes the surface of the wound bed from beneath. The debriding action may also contribute to the lowering of a wound's bacterial load by removal of dead tissue. Dead tissue is well known to provide an excellent medium for bacterial growth and increase the risk of infections if left in the wound. The amount of ‘free’ water in honey is measured as the water activity (a_(w)). Compositions of the invention may have a water activity of 0.7 or lower.

According to a preferred aspect of the invention, a composition of the invention may be used in a method of wound care, including the treatment of a wound, or the treatment or management of wound sepsis.

The wound may be an acute wound, chronic wound, surgical wound (for example, a Caesarean wound), chronic burn, or an acute burn. A composition of the invention may be used in the prophylactic prevention of wound sepsis. If a storage-stable composition of the invention is used, it will be appreciated that this may be diluted by liquid present at the wound site, which thereby leads to the release of hydrogen peroxide by the diluted composition.

According to the invention there is provided a method of treating a wound, which comprises administering a composition of the invention to the wound.

There is also provided according to the invention a composition of the invention for treatment of a wound.

Compositions of the invention may be used to treat wounds that are critically colonized. The term “critically colonized” is often used to refer to a wound that has reached a critical point at which bacteria begin to negatively affect the wound and begin to elicit signs of their presence. A critically colonized wound may indicate the presence of a biofilm. A bacterial load of greater than 10⁵ organisms/gram of tissue is often accepted as impeding wound healing (Siddiqui AR, Bernstein JM (2010) Chronic wound infection: Facts and controversies. Clinics in Dermatology 28: 519-26; Edmonds, M., & Foster, A. (2004). The use of antibiotics in the diabetic foot. Am J Surg, 187(5A), 25S-28S. Consequently, compositions of the invention may be used to treat wounds that have a bacterial load of greater than 10⁵ organisms/gram of tissue.

There is further provided according to the invention use of a composition of the invention in the manufacture of a medicament for treatment of a wound.

There is also provided according to the invention a method of treating inflammation, which comprises administering a composition of the invention to a site of inflammation.

There is also provided according to the invention a composition of the invention for treatment of inflammation.

There is further provided according to the invention use of a composition of the invention in the manufacture of a medicament for treatment of inflammation.

There is also provided according to the invention a method of stimulating tissue growth, which comprises administering a composition of the invention to a site in need of such stimulation.

There is also provided according to the invention a composition of the invention for stimulating tissue growth.

There is further provided according to the invention use of a composition of the invention in the manufacture of a medicament for stimulating tissue growth.

There is also provided according to the invention a method of debriding a wound, which comprises administering a composition of the invention to a wound in need of debridement.

There is also provided according to the invention a composition of the invention for debriding a wound.

There is further provided according to the invention use of a composition of the invention in the manufacture of a medicament for debriding a wound.

There is also provided according to the invention a method of deodorising a wound, which comprises administering a composition of the invention to a wound in need of deodorising.

There is also provided according to the invention a composition of the invention for deodorising a wound.

There is further provided according to the invention use of a composition of the invention in the manufacture of a medicament for deodordsing a wound.

For wound healing applications, compositions of the invention may be administered at an appropriate frequency determined by the healthcare provider. Suitably compositions of the invention may be administered at least every several days, for example every week, but preferably every day or every other day.

The amount of a composition of the invention administered will depend on many factors, such as the strength of the antimicrobial properties of the composition, and other wound healing properties of the composition, on the size of the wound, and on the age and condition of the subject to be treated. However, for many applications it is expected that administration of 2-100 g, or 5-100 g of a composition of the invention will be suitable, preferably 10-50 g.

According to the invention, there are also provided methods for making compositions of the invention.

According to the invention, there is provided a method for making a composition of the invention, comprising contacting an enzyme that is able to convert a substrate to release hydrogen peroxide, with a substrate for the enzyme and a superabsorbent component.

The enzyme and substrate may already be mixed, prior to contacting with the superabsorbent component. For example, the enzyme and substrate may be present in a liquid honey-based composition, such as SurgihoneyRO™, which is a honey containing added glucose oxidase, the honey having been pasteurised and sterilised by exposure to irradiation.

Alternatively, enzyme and substrate may be in a synthetic honey composition. The synthetic honey may comprise a purified enzyme, a purified substrate (or purified precursor-substrate) and a purified solute, as disclosed in any form herein. For instance, the solute may be in the form of a sugar or sugar derivative having a solubility of at least 100 g/100 g water at 20° C. and 1 atm. In a particularly preferred embodiment, the solute is fructose. So, in one embodiment, the method may involve using a composition comprising glucose, glucose oxidase and fructose. The solute may be at least 60% by dry weight of the composition. The substrate or precursor-substrate may be at least at 30% by dry weight of the composition. The combined dry weight of the substrate and the solute, or the precursor-substrate and the solute, may be at least 90%, preferably at least 95% of the composition. The total amount of sugar or sugar derivative in the composition may be at least 90%, by dry weight, preferably at least 95%, by dry weight.

The composition for use in the method may comprise 20% by weight, or less, of water. The composition for use in the method may comprise at least 10%, preferably at least 15% by weight of water.

The composition for use in the method may comprise at least 70%, more preferably at least 75%, by weight, or even more preferably at least 80%, by weight, of the substrate and solute combined, or the precursor-substrate and solute combined.

The composition for use in the method may be characterised in that the total amount of sugar or sugar derivative is at least 70%, more preferably at least 75%, by weight, or even more preferably at least 80%, by weight.

The composition for use in the method may be a liquid. If the composition for use in the method is a liquid, the method may comprise freeze-drying or lyophilising the composition to form a powder. If the method involves freeze-drying or lyophilising, a freeze-drying protective agent may be added to the composition. Suitable freeze-drying protective agents have been described herein.

If a composition of the invention has been formed by freeze-drying, it may comprise distinct powder particles of which each particle contains both the enzyme and the substrate (or precursor-substrate). If a composition of the invention has been formed by mixing powders rather than by freeze-drying, it may comprise distinct particles containing only enzyme and only substrate (or precursor-substrate).

In some embodiments, freezing and milling may take place before freeze-drying. This may allow more efficient drying.

Once the composition has been freeze-dried, it may then be contacted with a superabsorbent component, as described herein.

Alternatively, compositions of the invention may be formed by mixing powder forms of the enzyme, the substrate (or precursor-substrate) and the superabsorbent polymer.

Preferred embodiments of the invention are now described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 shows a photograph of a superabsorbent powder according to an embodiment of the invention, prior to addition of water;

FIG. 2 shows the resulting gel following addition of 15 ml of water to a superabsorbent powder according to an embodiment of the invention, with a hydrogen peroxide test strip indicating hydrogen peroxide production;

FIG. 3 shows the gel of FIG. 2 , in an inverted orientation.

FIG. 4 shows a gel following addition of 30 ml of water to a superabsorbent powder according to an embodiment of the invention;

FIG. 5 shows the gel of FIG. 4 in an inverted orientation;

FIG. 6 shows the particle size distributions of examples of superabsorbent powder compositions of the invention;

FIG. 7 shows a % strain sweep depicting the LVR for both extremes of current formulations including formulations which include maltodextrin and methylated R-Cyclodextrin;

FIG. 8 the effect of dilution upon the physical properties of examples of gels of the invention;

FIG. 9 shows the effect of increasing the amount of cross-linked sodium polyacrylate on viscoelastic properties of examples of gels of the invention;

FIG. 10 shows the effect of dilution at a fixed frequency (1 Hz) upon the storage modulus of examples of gels of the invention;

FIG. 11 shows a comparison of storage modulus values at different dilutions between different examples of gels of the invention;

FIG. 12 is a graph showing the effect of compositions suitable for use in forming examples of superabsorbent powders of the invention comprising glucose, glucose oxidase and fructose (SyntheticRO) on the growth of planktonic MRSA, compared to Surgihoney™, at various concentrations;

FIG. 13 is a graph showing the effect of sterile and non-sterile compositions suitable for use in forming examples of superabsorbent powders of the invention, comprising glucose, glucose oxidase and fructose (SyntheticRO) (buffered at pH 4.03) on the growth of planktonic MRSA, at various concentrations;

FIG. 14 is a graph showing the effect of sterile and non-sterile compositions suitable for use in forming examples of superabsorbent powders of the invention, comprising glucose, glucose oxidase and fructose (SyntheticRO) (unbuffered) on the growth of planktonic MRSA, at various concentrations;

FIG. 15 is a graph showing the effect of sterile and non-sterile compositions suitable for use in forming examples of superabsorbent powders of the invention, comprising glucose, glucose oxidase and fructose (SyntheticRO) (buffered at pH 7.04) on the growth of planktonic MRSA, at various concentrations;

FIG. 16 is a table showing the effect of sterile and non-sterile compositions suitable for use in forming examples of superabsorbent powders of the invention comprising glucose, glucose oxidase and fructose, on the MIC and MBC of planktonic MRSA, at various concentrations;

FIG. 17 shows the effect of compositions suitable for use in forming examples of superabsorbent powders of the invention, comprising glucose, glucose oxidase and fructose (SyntheticRO) on the growth of planktonic MRSA, compared to SurgihoneyRO, at various concentrations;

FIG. 18 shows the effect of SyntheticRO on the MIC and MBC of planktonic MRSA, compared to SurgihoneyRO, at various concentrations;

SPECIFIC EXAMPLES Example 1—Synthesis of Superabsorbent Powder

SurgihoneyRO (Sachet) or SyntheticRO (a mixture of purified glucose oxidase, purified glucose and purified fructose; see example 5) and either methylated β-Cyclodextrin (CycloLab R&D, UK) or Maltodextrin (Sigma Aldrich, UK) were first weighed out in equal proportions (50:50 ratio).

The desired amount (0.5, 1, 2 or 3 g) of cross-linked sodium polyacrylate (Sigma Aldrich. UK) was also weighed out.

All three components were then mixed together until a homogenous formulation was achieved. This formulation was then placed inside a freezer mill tube and submerged in liquid nitrogen for approximately 1 minute. The freezer mill tube was then placed in the freezer mill (SPEX SamplePrep). The freezer mill was run at a rate of 30 cycles per second for a total time of 3 minutes.

For compositions containing SurgihoneyRO, it was found that milling the mixture first allowed for a more complete drying process.

The samples were then transferred into the freeze drying chamber (Frozen in Time). The freeze drier cold trap was set to −55° C. and was at a pressure of 4.0×10⁻⁴ mbar. The sample was freeze dried for a total of 48 hours.

The samples were removed and sieved using 1000 μm and 500 μm gratings. Any powder that remained in the sieves was crushed using a pestle and mortar and ran through the sieves again. The powder was then sealed in a pot containing silica gel beads which act as a desiccant.

Example 2—Formation of Gels

To demonstrate formation of gels, water was added to a powder containing 40:60 SurgihoneyRO™ to cyclodextrin composition containing 3 wt % sodium polyacrylate.

FIG. 1 shows 1 g of the powder prior to addition of water, in a weighing boat.

FIG. 2 shows the resulting gel following addition of 15 ml of water. It also shows a hydrogen peroxide test strip indicating the production of hydrogen peroxide by the gel. FIG. 3 shows the same gel, but in an inverted orientation. This demonstrates how the gel may readily adhere to a surface.

FIG. 4 shows the gel following addition of 30 ml of water, and FIG. 5 shows the same gel in an inverted orientation.

Example 3—Particle Size Analysis

An instrument called QICPIC (Sympatec, UK) was employed, which uses of dynamic image analysis to size particles. High speed image analysis used a pulsed light source with illumination times of less than 1 nanosecond. The particles are optically frozen while a high-resolution, high-speed camera captures the particle projections. Algorithms built into the instrument software evaluate the particles giving statistically relevant results. The following parameters were used in order to determine particle size:

-   -   Calculation mode: EQPC—this mode is used to calculate the         diameter of a circle that has the same area as the projection         area of the particle.     -   Trigger condition: start 0s, valid 300s     -   Dispersing method: 2 mm 25% 4 mm     -   Frame rate: 100 fps     -   Height of fall: 40.00 cm     -   Feeder: Vibrate     -   Feed rate: 25.00%     -   Gap height: 2.00 mm

The amount of superabsorbent polymer in the compositions and the type of freeze-drying protective agent was varied in order to establish the impact of varying these parameters on the properties of the compositions.

The following compositions were tested, and their peak particle distributions and sphericities were established.

-   -   A superabsorbent reactive oxygen powder containing 47.8 wt. %         methylated β-Cyclodextrin, 47.6 wt % SurgihoneyRO and 4.8 wt. %         cross-linked sodium polyacrylate.     -   This composition contains a peak particle size distribution at         204.5 μm and a peak sphericity distribution at 0.9.     -   A superabsorbent reactive oxygen powder containing 45.5 wt. %         methylated β-Cyclodextrin, 45.5 wt. % SurgihoneyRO and 9.1 wt. %         cross-linked sodium polyacrylate.     -   This composition contains a peak particle size distribution at         204.5 μm and a peak sphericity distribution at 0.9.     -   A superabsorbent reactive oxygen powder containing 41.7 wt %         methylated β-Cyclodextrin, 41.7 wt. % SurgihoneyRO and 16.7 wt.         % cross-linked sodium polyacrylate.     -   This composition contains a peak particle size distribution at         186.4 μm and a peak sphericity distribution at 0.9.     -   A superabsorbent reactive oxygen powder containing 38.5 wt. %         methylated O-Cyclodextrin, 38.5 wt. % SurgihoneyRO and 23.1 wt.         % cross-linked sodium polyacrylate.     -   This composition contains a peak particle size distribution at         204.5 μm and a peak sphericity distribution at 0.9.     -   A superabsorbent reactive oxygen powder containing 38.5%         methylated β-Cyclodextrin, 38.5% wt % SyntheticRO and 23.1 wt. %         cross-linked sodium polyacrylate     -   This composition contains a peak particle size distribution at         540.5 μm and a peak sphericity distribution at 0.82.     -   A superabsorbent reactive oxygen powder containing 47.6 wt. %         maltodextrin, 47.6 wt. % SurgihoneyRO and 4.8 wt. % cross-linked         sodium polyacrylate.     -   This composition contains a peak particle size distribution at         405.7 μm and a peak sphericity distribution at 0.85.     -   A superabsorbent reactive oxygen powder containing 45.5 wt. %         maltodextrin, 45.5 wt % SurgihoneyRO and 9.1 wt. % cross-linked         sodium polyacrylate.     -   This composition contains a binomial distribution with peak         particle size distributions at 445.0 μm and 2107.4 μm, a peak         sphericity distribution at 0.85.     -   A superabsorbent reactive oxygen powder containing 41.7 wt. %         maltodextrin, 41.7 wt. % SurgihoneyRO and 16.7 wt. %         cross-linked sodium polyacrylate.     -   This composition contains a peak particle size distribution at         445.0 μm a peak sphericity distribution at 0.85.     -   A superabsorbent reactive oxygen powder containing 38.5 wt. %         maltodextrin, 38.5 wt. % SurgihoneyRO and 23.1 wt. %         cross-linked sodium polyacrylate.     -   This composition contains a binomial distribution with peak         particle size distributions at 445.0 μm and 2107.4 μm a peak         sphericity distribution at 0.85.     -   A superabsorbent reactive oxygen powder containing 38.5 wt. %         maltodextrin, 38.5 wt. % SyntheticRO and 23.1 wt. % cross-linked         sodium polyacrylate.     -   The composition contains a polymodal distribution with peak         particle size distributions at 540.5 μm, 968.4 μm and 1428.5 μm;         and two peak sphericity distribution at 0.45 and 0.85.

FIG. 6 a) illustrates the particle size distributions of each composition containing β-cyclodextrin sodium polyacrylate and SurgihoneyRO/SyntheticRO. FIG. 6 b) Illustrates the particle size distributions of each composition containing maltodextrin, sodium polyacrylate and SurgihoneyRO/SyntheticRO.

The results obtained suggest the following:

-   -   Increasing the wt % of cross-linked sodium polyacrylate may not         affect particle size.     -   Compositions containing methylated β-cyclodextrin may have a         smaller average particle size than those that contain         maltodextrin.     -   Formulations that contain methylated A-cyclodextrin may produce         more spherical particles.     -   Formulations containing Maltodextrin appear to aggregate or         agglomerate to form larger particles post-sieving.

Example 4—Gel Rheology Analysis

Firstly the linear viscoelastic region (LVR) was determined for all of the tested powder gels. The LVR is determined so that the material behaves linearly and an out of phase sinusoidal shear stress response is produced. This was achieved by conducting a strain sweep on a Rheometer (TA instruments, UK) using a 40 mm steel sand blasted plate geometry in parallel to another sand blasted steel plate.

FIG. 7 shows a % strain sweep depicting the LVR for both extremes of tested formulations including formulations which include maltodextrin (MD) and methylated β-Cyclodextrin (CD).

The strain sweep was conducted under the following conditions:

-   -   % strain range was set logarithmically from 0.01 to 50.0 with 10         points measured per decade.     -   Temperature set to 34° C. relevant to the final topical         application with an equilibration time of 2 minutes.     -   The frequency was kept constant at 1 Hz     -   Geometry gap was set at 1000 μm

The strain sweep identified a % strain that fell into the LVR for all of the samples; this was found to be 0.5% strain.

Frequency sweeps were then carried out at this % strain and the following conditions:

-   -   Frequency range was set logarithmically from 0.1 and 100 Hz with         10 points measured per decade.     -   Temperature set to 34° C. relevant to the final topical         application with an equilibration time of 2 minutes.

The same compositions as those in Example 3 were used to form gels by adding varying amounts of water (5 ml, 10 ml or 20 ml).

FIG. 8 a) shows the effect of dilution upon the physical properties of the gel formed from a composition containing 38.5 wt. % methylated β-cyclodextrin, 38.5 wt. % SurgihoneyRO and 23.1 wt. % cross-linked sodium polyacrylate, at a range of frequencies. FIG. 8 b) shows the same composition but with syntheticRO, rather than SurgihoneyRO.

The results indicate how shows how the gels formed may be more elastic than viscous (higher G′ (storage modulus) than G″ (loss modulus)), over the range of frequencies; and how there may be a low frequency dependency. Similar effects were observed for the other compositions.

FIG. 9 shows the effect of increasing the amount of cross-linked sodium polyacrylate in maltodextrin: SurgihoneyRO/SyntheticRO compositions containing 4.8 wt. %, 9.1 wt. %, 16.7 wt. % and 23.1 wt. % upon the storage modulus (G′). The gels were formed by adding 5 ml of distilled water. FIG. 9 shows how an increase in cross-linked sodium polyacrylate may increase the stiffness of the gel that is formed. Similar effects were observed for the other compositions.

FIG. 10 shows the effect of dilution at a fixed frequency (1 Hz) upon the storage modulus of the gel containing varying amounts of cross-linked sodium polyacrylate in maltodextrin: SurgihoneyRO/SyntheticRO formulations.

FIG. 11 a) shows a comparison of storage modulus values at different dilutions between gels formed from compositions containing maltodextrin: SurgihoneyRO and compositions containing methylated β-cyclodextrin: SurgihoneyRO, the compositions containing 16.7 wt. % cross-linked sodium polyacrylate. FIG. 11 b) shows results from the same formulations, but which contain SyntheticRO rather than SurgihoneyRO.

The results obtained suggest the following:

-   -   An increase in cross-linked sodium polyacrylate may increase the         stiffness of the gel;     -   There is a low frequency dependency;     -   Samples may be more elastic than viscous;     -   Gels containing SyntheticRO may have a higher G′ and G″ than         those which contain SurgihoneyRO;     -   There may be no significant difference between the rheology of         the formulations that contain maltodextrin or cyclodextrin;     -   Cyclodextrin-based formulations may dissolve more readily upon         application to water than those which contain maltodextrin.

Example 5—Synthetic Honey Compositions (Also Known as SyntheticRO

Samples with batch number “RO” contain no glucose oxidase.

Samples with batch number “RO1” contain 50 ppm glucose oxidase.

Samples with batch number “R02” contain 1000 ppm glucose oxidase.

A. pH 4.03 Buffered Samples A1. Batch No NB01p43RO

-   -   Non sterile

Material Weight fraction Fructose 52.0% Glucose 31.0% 50 mMol Citric acid/NaOH buffer pH 4.03 17.0%

Description

Non sterile base buffered saccharide solution.

A2. Batch no NB01p43RO

-   -   Sterile

Material Weight fraction Fructose 52.0% Glucose 31.0% 50 mMol Citric acid/NaOH buffer pH 4.03 17.0%

Description Sterile base buffered saccharide solution

A3. Batch no NB01p44RO1

-   -   Non Sterile

Material Weight fraction Fructose 52.0% Glucose 31.0% 50 mMol Citric acid/NaOH buffer pH 4.03 17.0%

Description

Non sterile base buffered RO1 saccharide solution.

A4. Batch no NB01p44RO1

-   -   Sterile

Material Weight fraction Fructose 52.0% Glucose 31.0% 50 mMol Citric acid/NaOH buffer pH 4.03 17.0%

Description

Non sterile base buffered R02 saccharide solution.

A6. Batch no NB01p44RO2

-   -   Sterile

Material Weight fraction Fructose 52.0% Glucose 31.0% 50 mMol Citric acid/NaOH buffer pH 4.03 17.0%

Description

Non sterile base buffered R02 saccharide solution.

A6. Batch no NB01p43RO2

-   -   Sterile

Material Weight fraction Fructose 52.0% Glucose 31.0% 50 mMol Citric acid/NaOH buffer pH 4.03 17.0% GOX enzyme N/A

Description Sterile base buffered R02 saccharide solution

B. Unbuffered Samples B1. Batch no NB01p51RO

-   -   Non sterile

Material Weight fraction Fructose 52.0% Glucose 31.0% Water 17.0%

Description

Non sterile base buffered RO1 saccharide solution.

B2. Batch no NB01p51RO1

-   -   Sterile

Material Weight fraction Fructose 52.0% Glucose 31.0% Water 17.0%

Description Sterile base buffered saccharide solution

B3. Batch no NB01p51RO1

-   -   Non sterile

Material Weight fraction Fructose 52.0% Glucose 31.0% Water 17.0%

Description

Non sterile base buffered R01 saccharide solution.

B4. Batch no NB01p51RO1

-   -   Sterile

Material Weight fraction Fructose 52.0% Glucose 31.0% Water 17.0%

Description

Sterile base buffered RO1 saccharide solution

B5. Batch no NB01p51RO2

-   -   Non sterile

Material Weight fraction Fructose 52.0% Glucose 31.0% Water 17.0%

Description

Non sterile base buffered R02 saccharide solution.

B6. Batch no NB01p51RO2

-   -   Sterile

Material Weight fraction Fructose 52.0% Glucose 31,0% Water 17.0%

Description

Sterile base buffered R02 saccharide solution

C. pH 7.04 Buffered Samples C1. Batch no NB01p57RO

-   -   Non sterile

Material Weight fraction Fructose 52.0% Glucose 31.0% 50 mMol Citric acid/NaOH buffer pH 7.04 17.0%

Description

Non sterile base buffered saccharide solution

C2. Batch no NB01p57RO

-   -   Sterile

Material Weight fraction Fructose 52.0% Glucose 31.0% 50 mMol Citric acid/NaOH buffer pH 7.04 17.0%

Description

Sterile base buffered saccharide solution

C3. Batch no NB01p57RO1

-   -   Non sterile

Material Weight fraction Fructose 52.0% Glucose 31.0% 50 mMol Citric acid/NaOH buffer pH 7.04 17.0%

Description

Non sterile base buffered RO1 saccharide solution.

C4. Batch no NB01p57RO1

-   -   Sterile

Material Weight fraction Fructose 52.0% Glucose 31.0% 50 mMol Citric acid/NaOH buffer pH 7.04 17.0%

Description

Sterile base buffered RO1 saccharide solution

C5. Batch no NB01p57RO2

-   -   Non sterile

Material Weight fraction Fructose 52.0% Glucose 31.0% 50 mMol Citric acid/NaOH buffer pH 7.04 17.0%

Description

Non sterile base buffered R02 saccharide solution.

C6. Batch no NB01p57RO2

Material Weight fraction Fructose 52.0% Glucose 31.0% 50 mMol Citric acid/NaOH buffer pH 7.04 17.0%

Description

Sterile base buffered R02 saccharide solution

Example 6—Efficacy of Synthetic Honey Compositions Against Planktonic MRSA

MIC and MBC were assessed for the RO1 samples (containing 50 ppm glucose oxidase) and compared to Surgihoney™ (also containing 50 ppm glucose oxidase). See Andrews J. M. Journal of Antimicrobial Chemotherapy (2001) 48, suppl. S1, 5-16.

The results are shown in FIGS. 1 to 5 .

The results show that, like Surgihoney, synthetic compositions containing glucose, glucose oxidase and fructose are able to inhibit microbial growth.

Out of all of synthetic compositions, the synthetic composition buffered at pH7.04 had the most effective MIC. Sterilised compositions were more effective than non-sterilised compositions, and synthetic composition buffered at pH7.04 synthetic had the most effective MBC when compared to other synthetic compositions and even when compared to SurgihoneyRO.

FIGS. 17 (a to d) and 18 show MIC and MBC results including SurgihoneyRO (RO2) samples and synthetic R02 samples. 

1-80. (canceled)
 81. A sterile composition comprising: an enzyme that is able to convert a substrate to release hydrogen peroxide; a substrate for the enzyme; and a water-absorbing polymer, wherein the composition is in the form of a powder which has a mean and/or modal particle diameter of 50 to 3000 μm, and wherein the composition does not comprise honey.
 82. A composition according to claim 81, wherein the water-absorbing polymer has an absorption capacity of at least 1 g/g.
 83. A composition according to claim 82, wherein the absorption capacity is in respect of deionized water or a 0.9% w/w saline solution.
 84. A composition according to claim 81, comprising substantially no peroxidase.
 85. A composition according to claim 81, comprising polyethylene glycol.
 86. A composition according to claim 81, wherein the powder contains less than 10% of particles with a diameter of 50 μm or less.
 87. A composition according to claim 81, wherein the enzyme is an oxidoreductase enzyme and the substrate is a sugar.
 88. A composition according to claim 87, wherein the oxidoreductase enzyme is glucose oxidase and the sugar is glucose.
 89. A composition according to claim 81, comprising substantially no zinc oxide.
 90. A composition according to claim 81, comprising hydrogen peroxide at a level less than 1 ppm.
 91. A composition according to claim 81, comprising a blood clotting agent.
 92. A composition according to claim 81, comprising 1 to 50% by weight of the water-absorbing polymer.
 93. A composition according to claim 81, comprising 25% to 75% by weight of the water-absorbing polymer.
 94. A composition according to claim 81, comprising a salt.
 95. A composition according to claim 81, comprising a buffer.
 96. A wound dressing comprising a composition according to claim 81 and a wound dressing material.
 97. A wound dressing according to claim 96, wherein the wound dressing material is impregnated with the composition or the composition is immobilised on the wound dressing material.
 98. An airtight container comprising a composition according to claim
 81. 99. A method of preventing, treating, or ameliorating a microbial infection, the method comprising administering a composition according to claim 81, to a subject in need of such prevention, treatment, or amelioration.
 100. A method of treating a wound, the method comprising administering to the wound a composition according to claim
 81. 